Desiccation cracking of soil affected by actions of climate is a common phenomenon in nature. The presence of cracks can dramatically weaken the engineering properties of soil and cause many geotechnical and geological engineering problems. In this study, a refined monitoring method of the dynamic process of soil desiccation cracking using electrical resistivity tomography (ERT) was proposed to determine the development of the cracking networks in clayey soil. The model test and in-situ test were carried out to monitor the process of soil cracking separately. Self-developed resistance measuring system was applied to continuously collecting the current-potential difference data. The data were then processed and inverted using a self-developed system named FemERT (finite element method electrical resistivity tomography) to obtain spatial distribution characteristics of the cracking networks at different periods. The results show that: (1) ERT can achieve the refined monitoring of the soil cracking process and can monitor the geometric morphology of three-dimensional crack networks. The identification accuracy of crack width and depth can reach millimeter level and centimeter level respectively. (2) The difference in sensitivity distribution of ERT can explain the influence of cracking on soil resistivity. The measured resistance curves show different features according to the position of the crack formatting. (3) The interpreted resistivity and its relative change rate (Rev) can directly describe the spatial geometric morphology of the cracking networks at different stages, highlighting the influence of the dynamic development process of cracking on the electrical conductivity of soils.